Colorectal cancer, also known as large bowel cancer, is when malignant cancer cells grow in the wall of the large bowel. This includes the large intestine, and rectum, which are all part of the lower digestive tract. Cancers that affect the small bowel (or small intestine) are very rare. (See small bowel cancer.)
Colorectal cancer occurs when the cells of the large bowel lining begin to grow uncontrollably and turn into a cell clump called a polyp or an adenoma. Most polyps are benign and are not malignant or cancerous. However, when polyps are undetected they can become cancerous. Most bowel cancers originate from cancerous polyps that spread to other organs.
The most common type of bowel cancer is called an adenocarcinoma, named after the glandular cells in the lining of the bowel where the cancer first develops. Other rarer types include hamartomas, mesenchymal tumours, neuroendocrine tumour, and lymphomas.
Early stages of colorectal cancer often do not cause any symptoms or only discovered by routine screening. Sometimes they can present with non-specific symptoms, which can be commonly found in other illnesses, such as haemorrhoids.
Colorectal or bowel cancer symptoms may include:
- Blood in stool or on the toilet paper
- Change in bowel habits. This includes more frequent bowel movements, constipation or diarrhoea.
- Change in appearance and consistency of bowel movements.
- Changes in bowel function, such as feeling bowel hasn’t emptied completely even after a bowel movement.
- Feeling of bloating
- Unexplained weight loss
- Unexplained weakness or fatigue
- Rectal or anal pain
- A lump in the abdomen
- Pain, cramps or swelling in the abdomen
- Iron deficiency anaemia (low red blood cell count)
If you experience any of these symptoms or have concerns, please contact your general practitioner (GP).
It is projected that colorectal cancer will be the fourth most commonly diagnosed type of cancer in Australia and the second leading cause of cancer death in 2023 with an estimated 15,367 new cases diagnosed. Males are 1.25 times as likely to be diagnosed with colorectal cancer as females. The risk of colorectal cancer increases with age.
Individuals diagnosed with colorectal cancer have a 70.9% chance of surviving longer than five years.
If detected early, colorectal cancer is one of the most curable types of cancer and responds well to treatment, especially if the cancer has not spread.
For more information see below in the screening for colorectal cancer tab.
There are lifestyle and health factors that can increase the risk of developing colorectal cancer.
Risk factors include:
- Older age (50 years and over)
- Diet high in fat and red meat (especially processed meat, such as salami)
- Heavy drinking of alcohol
- Family history of bowel cancer or polyps (However, more than 75% of people who develop bowel cancer do not have a family history of bowel cancer)
- Inherited genetic conditions (have been linked to 5-6% of bowel cancers), including Familial Adenomatous Polyposis and Lynch Syndrome.
- Pre-existing inflammatory bowel diseases such ulcerative colitis or Crohn’s disease
- Past medical history of polyps in the bowel.
The type of tests for colorectal cancer will vary depending on the symptoms. Early diagnosis of colorectal cancer is possible through a screening test called the faecal occult blood test (FOBT). The FOBT looks for blood in stool samples, possibly caused by polyps and early symptoms of colorectal cancer. This is free and available for individuals over 50. (See in the tab below; screening for colorectal cancer.)
When there is suspicion of a possible colorectal cancer diagnosis, the medical practitioner will first conduct a physical examination to check the abdomen for swelling. A digital rectal exam may also be done where the doctor checks for swelling in the anus and rectum. Examinations also include blood tests to check for anaemia.
A colonoscopy also allows the doctor to examine the entire length of the large bowel. This can help detect polyps and any abnormal body tissue. This is done using a thin flexible tube with a camera, called a colonscope, inserted into the anus, rectum and colon. During the procedure, the doctor may also take a small sample of tissue, called a biopsy, for examination under a microscope to see if there are any cancer cells.
Other imaging technology may be used to get a clearer picture for doctors to see if there is any evidence of cancer. This may include computed tomography/positron emission tomography (CT/PET scans) or Magnetic Resonance Imaging (MRI).
Surgery is the most common type of treatment for colorectal cancer. However, this depends on the location of the cancer and whether it has presented at an advanced stage. Treatment options include surgery, radiotherapy or chemotherapy. If the cancer is found at an early stage, the chance of a full recovery is high.
In some cases, polyps can be removed during a colonoscopy, and if the biopsy confirms it is not cancerous, no further treatment is needed. However, regular check-ups are recommended.
The most common form of surgery to remove cancer in the colon is called a colectomy. The amount of colon removed during surgery depends on the location and how extensive the cancerous area is. Lymph nodes near the colon and part of the bowel may also be removed. If the cancer is in the rectum, the specific location will determine how extensive and complex the surgery will be. If it is a small area and the cancer hasn’t spread, rectal cancer can be removed locally. In some cases, all of the colon and rectum are removed.
Chemotherapy and radiotherapy may be given during or after surgery to kill cancerous cells. Neoadjuvant chemotherapy or radiotherapy is given before surgery to shrink and kill the cancer cells and to help with removal of the tumour. Adjuvant chemotherapy or radiotherapy is given after surgery to destroy any remaining cancer cells.
Australia has a National Bowel Cancer Screening Program that provides free and easy bowel cancer tests for individuals aged over 50.
The program’s aim is early detection of bowel cancer in individuals before any serious symptoms appear. The screening test is called a Faecal Occult Blood Test (FOBT), which detects blood in stool samples. The test does not diagnose bowel cancer, but can find tiny traces of blood in stool samples, which may be an early sign of disease. The results will indicate if a further test is needed to rule out bowel cancer.
Research has shown screening for bowel cancer, using the FOBT, can reduce bowel cancer deaths by 15 to 25%.
You can learn more about the National Bowel Cancer Screening Program here.
Avoiding the risk factors can help to reduce the chance of developing colorectal cancer. Protective steps include being physically active and maintaining a healthy body weight. This includes changes in lifestyle habits, such as having a diet high in fibre, eating fresh fruit and vegetables and cutting down on processed meat.